国家地理 龙卷风的形成

Call them twisters or tornadoes². They are nature's most violent storms with swirling³ winds that can top 300 miles per hour. About 800 twisters sweep through the US every year, more than anywhere else in the world. The hardest-hit area is a swath of the Great Plains from Texas to South Dakota, known as Tornado¹ Alley⁴. Here, warm air flows up from the Gulf⁵ of Mexico in the spring and summer and crashes into cold air pushing down from Canada. The meeting produces violent thunderstorms called supercells.

龙卷风是大自然最为猛烈的风暴，他们自带旋转的狂风，时速最高可达300英里。每年，美国都会遭受近800场龙卷风，没有哪个地方的遭受次数比美国更高。得克萨斯州到南达科塔之间，受创最为惨重的是北美大平原了，这里是龙卷道。这里春天和夏天的时候，暖空气会从墨西哥湾上升，然后与来自加拿大的冷空气相撞。交汇处会产生强烈的雷暴，也称超级单体。

Scientists don't completely understand how or when tornados⁶ form, but they do know a supercell like this one can produce a twister if the conditions are right. As more moist air flows into a storm, it gets pushed up and twisted by upper level winds. As this rotating column of air gathers force, conditions are right for a collision below. When rain cooled downdrafts hit warm air near the ground, a low hanging revolving⁷ cloud forms beneath the cell. A tornado is imminent⁸.

科学家不是十分清楚龙卷风形成的方式和时间点，但他们可以肯定的是：一旦条件合适，类似这样的超级单体就可以产生龙卷风。湿空气进入风暴里之后，就会受到推力作用，被上层的风带动着旋转。这种旋转气柱的力量越来越大，等条件合适的时候，就会发生下面的碰撞。经过雨水冷却的下降气流与地表附近的暖空气碰撞，单体下面的低空就会产生旋转的云。这时候就快产生龙卷风了。

Tornadoes don't last long, anywhere from 20 seconds to an hour. But it can take years to recover from the devastation⁹. These storms kill nearly 90 people each year in the US and cause millions of dollars worth of damage. When a tornado is spotted¹⁰, experts advise going to a basement, staying away from any windows or climbing into a first floor bathtub. While most people run for safety when a twister appears, some scientists actually race to need it. These storm chasers hunt down tornadoes, trying to get right in the twister's path.

龙卷风持续时间很短，从20秒到1小时不等。但其造成的损害却是数年才能修复的。每年，龙卷风都会导致近90人死亡，其造成的损失达数百万美元。一旦看到龙卷风，专家建议去地下室待着，避开窗户，也不要在一层的浴缸里待着。大多数人对龙卷风避犹不及，一心想着保平安，但有些科学家却对龙卷风趋之若鹜。他们苦苦追寻龙卷风，试图与龙卷风打个照面儿。

They encounter incredible cloud movement, torrential rain, severe winds and hail, lightening, breathtaking storm structures. When they finally locate a twister, they measure it using special tools. These scientists hope to someday predict exactly when and where tornadoes will strike. Little can prevent the damage caused by tornadoes, but better forecasting could save more lives, giving survivors¹¹ the chance to rebuild after living through one of the most violent storms on earth.

他们会遇到难以想象的云体移动、倾盆大雨、强风、冰雹、闪电以及令人叹为观止的风暴。一旦他们发现了龙卷风，就会用特殊工具来进行测量。这些科学家希望有一天可以准确预测龙卷风发生的时间和地点。很难避免龙卷风造成损失，但预测能力的提高可以挽救更多的生命，让幸存者有机会重建家园，就算他们曾经遭遇了世界上最可怕的风暴之一。

1 tornado   

n.飓风，龙卷风

参考例句：

• A tornado whirled into the town last week.龙卷风上周袭击了这座城市。
• The approaching tornado struck awe in our hearts.正在逼近的龙卷风使我们惊恐万分。

2 tornadoes   

n.龙卷风，旋风( tornado的名词复数 )

参考例句：

• Tornadoes, severe earthquakes, and plagues create wide spread havoc. 龙卷风、大地震和瘟疫成普遍的毁坏。 来自互联网
• Meteorologists are at odds over the working of tornadoes. 气象学者对龙卷风的运动方式看法不一。 来自互联网

3 swirling   

v.旋转，打旋( swirl的现在分词 )

参考例句：

• Snowflakes were swirling in the air. 天空飘洒着雪花。 来自《现代汉英综合大词典》
• She smiled, swirling the wine in her glass. 她微笑着，旋动着杯子里的葡萄酒。 来自辞典例句

4 alley   

n.小巷，胡同；小径，小路

参考例句：

• We live in the same alley.我们住在同一条小巷里。
• The blind alley ended in a brick wall.这条死胡同的尽头是砖墙。

5 gulf   

n.海湾；深渊，鸿沟；分歧，隔阂

参考例句：

• The gulf between the two leaders cannot be bridged.两位领导人之间的鸿沟难以跨越。
• There is a gulf between the two cities.这两座城市间有个海湾。

6 tornados   

n.龙卷风，旋风( tornado的名词复数 )

参考例句：

• And the national weather service reports several tornados touch down. 国家气象中心报告预测龙卷风将来袭。 来自互联网
• They had stock footage of lightning, tornados, and hurricanes. 他们存有关于闪电、龙卷风和飓风的电影胶片。 来自互联网

7 revolving   

adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想

参考例句：

• The theatre has a revolving stage. 剧院有一个旋转舞台。
• The company became a revolving-door workplace. 这家公司成了工作的中转站。

8 imminent   

adj.即将发生的，临近的，逼近的

参考例句：

• The black clounds show that a storm is imminent.乌云预示暴风雨即将来临。
• The country is in imminent danger.国难当头。

9 devastation   

n.毁坏；荒废；极度震惊或悲伤

参考例句：

• The bomb caused widespread devastation. 炸弹造成大面积破坏。
• There was devastation on every side. 到处都是破坏的创伤。 来自《简明英汉词典》

10 spotted   

adj.有斑点的，斑纹的，弄污了的

参考例句：

• The milkman selected the spotted cows,from among a herd of two hundred.牛奶商从一群200头牛中选出有斑点的牛。
• Sam's shop stocks short spotted socks.山姆的商店屯积了有斑点的短袜。

11 survivors   

幸存者，残存者，生还者( survivor的名词复数 )

参考例句：

• The survivors were adrift in a lifeboat for six days. 幸存者在救生艇上漂流了六天。
• survivors clinging to a raft 紧紧抓住救生筏的幸存者